1. Field
Disclosed herein is a tire tread for a passenger vehicle comprising particular means for alerting an observer on the state of wear of this tire.
2. Description of Related Art
Document EP 1066991 A2 discloses a tire tread provided with a plurality of sipes making it possible to obtain an item of information on the state of wear of the tire during the use of the said tire.
“Tire” means all types of elastic tires subjected, when running, to a pressure that may or may not be internal.
“Tire tread” means a quantity of rubbery composition delimited by lateral surfaces and by two main surfaces of which one is designed to come into contact with a ground when the tire runs.
“Tread surface” means the surface formed by the points of the tire tread that come into contact with the ground when the tire runs.
“Sipe” is a cut-out of which the material faces touch one another in usual running conditions. Generally, the width of a sipe is less than 2 mm.
In document EP 1066991 A2, sipes extending in the depth of the tread emerge on the tread surface to form the message “very good condition”.
The sipe forming the word “very” extends in a lesser depth than the word “good”. In the same manner, the word “good” extends in a lesser depth than the word “condition”.
Therefore, in the new state, it is possible to read the message “very good condition” in its entirety on the tread surface.
When the tire tread reaches a first rate of wear, the word “very” can no longer be read on the tread surface.
“Wear rate” means the ratio between a thickness that the tread has lost through wear and the total thickness that the tread can lose before having to be replaced.
Therefore, a wear rate of 25% means that the tread has lost a quarter of the rubbery composition to be worn.
In document EP 1066991 A2, when the tire tread reaches a second wear rate greater than the first wear rate, the word “good” can no longer be read on the tread surface.
Finally, when the tire tread reaches a third wear rate greater than the second wear rate, the word “condition” can no longer be read on the tread surface.
The disappearance of the whole message “very good condition” on the tread surface means that it is necessary to replace the tire.
The wear indicator disclosed in document EP 1066991 A2 has a certain number of drawbacks.
First of all, the disappearance of the message on the tread surface may not sufficiently alert the observer to the need to change the tire. Specifically, the disappearance of the message makes the tread surface visually more even. The observer may then wrongly believe that the tire is still operational since nothing indicates the contrary to him.
Moreover, the sipes forming the message may be filled in by mud or dust during the use of the tire. Consequently, the legibility of the message on the tread surface is limited.
Finally, the use of a wear indicator according to the document disclosed above requires the tread to be provided with a plurality of sipes; this may then cause irregular wear of the tread close to these sipes.
There is therefore a need to provide a wear indicator making it possible to solve the problems explained above.